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Cannot delete instance of model referenced by ManyToManyField

See original GitHub issue

I have the following models:

models.py

class School(TenantModel):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    name = models.CharField(max_length=100)
    tenant_id = 'id'

class User(AbstractBaseUser, PermissionsMixin):
    email = models.EmailField(max_length=255, unique=True)
    objects = UserManager()

    USERNAME_FIELD = 'email'

class UserProfile(TenantModel):
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='userprofiles')
    school = models.ForeignKey(School, on_delete=models.CASCADE, related_name='members')
    departments = models.ManyToManyField('Department', blank=True, related_name="members")
    is_admin = models.BooleanField(default=False)
   
    tenant_id = 'school_id'

class Department(TenantModel):
    name = models.CharField(max_length=500, unique=True)
    school = models.ForeignKey(School, on_delete=models.CASCADE)

    tenant_id = 'school_id'

Attempting to delete a Department instance throws the error “TypeError: related_objects() takes 3 positional arguments but 4 were given”. This happens even if a tenanted through model is used.

Traceback

  File "/Users/alex/Library/Mobile Documents/com~apple~CloudDocs/Documents/bunsen/backend/schools/tests/test_schools_api.py", line 171, in test_delete_department_successful
    response = self.client.delete(
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/test.py", line 317, in delete
    response = super().delete(
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/test.py", line 219, in delete
    return self.generic('DELETE', path, data, content_type, **extra)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/test.py", line 231, in generic
    return super().generic(
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/test/client.py", line 470, in generic
    return self.request(**r)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/test.py", line 283, in request
    return super().request(**kwargs)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/test.py", line 235, in request
    request = super().request(**kwargs)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/test/client.py", line 709, in request
    self.check_exception(response)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/test/client.py", line 571, in check_exception
    raise exc_value
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/core/handlers/base.py", line 179, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/viewsets.py", line 114, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/views.py", line 505, in dispatch
    response = self.handle_exception(exc)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/views.py", line 465, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/views.py", line 476, in raise_uncaught_exception
    raise exc
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/views.py", line 502, in dispatch
    response = handler(request, *args, **kwargs)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/mixins.py", line 91, in destroy
    self.perform_destroy(instance)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/rest_framework/mixins.py", line 95, in perform_destroy
    instance.delete()
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/db/models/base.py", line 943, in delete
    collector.collect([self], keep_parents=keep_parents)
  File "/Users/alex/.local/share/virtualenvs/backend-xQfT061F/lib/python3.8/site-packages/django/db/models/deletion.py", line 313, in collect
    sub_objs = self.related_objects(related_model, related_fields, batch)
TypeError: related_objects() takes 3 positional arguments but 4 were given```

Issue Analytics

State:
Created 3 years ago
Comments:6 (4 by maintainers)

Top GitHub Comments

1reaction

louiseGrandjonccommented, Aug 25, 2020

The through model is not essential. It’s required for distributed databases though. So if you decided to shard your database on the column school_id and wanted to distribute the members relation. If you’re not using a distributed database, then it works perfectly fine 😃

1reaction

pickyuptruckcommented, Aug 24, 2020

one final question: are through models essential? Things seem to be working fine without them

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